Retrieving only the superclass in hibernate

Question

I have a superclass and a subclass mapped to have a table for each class like this

@Entity
@Table(name="superclass_table") 
@Inheritance(strategy=InheritanceType.JOINED )
public class SuperClass {    
}

@Entity
@Table(name="subclass_table")
public class SubClass extends SuperClass {
}

When I make

session.createCriteria(SuperClass.class).list();

I get everything that is in the superclass_table.

I want to get only the objects that is in the superclass_table but isn't in the subclass_table.